When Mark Zuckerberg first decided seven years ago to learn Mandarin, the official dialect of mainland China, he reportedly did it to impress the family of his then long-time girlfriend and now wife, Priscilla Chan.

Nevertheless, Zuckerberg found learning the language useful for business, especially when it comes to trying to get Facebook into the Chinese market.

Chinese President Xi Jinping gave a speech at the end of last month at one of China’s elite universities on the country’s continuing openness to foreign companies: Zuckerberg was in the audience. Different from Tim Cook, who was also present, Zuckerberg probably did not rely as much on interpreters. He has met Xi several times during the past few years, in hopes of him lifting the ban on using Facebook in China.

Facebook was first blocked in China in the summer of 2009 after what Chinese authorities called a terrorist attack in West China. The website was said to be used by the attackers, which gave the Chinese government enough reason to prohibit all access to the site from mainland China. The ban does not cover Hong Kong and Macau, which are districts given special status in China and run a relatively different political system where the central government’s regulations often do not apply.

Users in China have had to use virtual private networks to visit Facebook and other sites like Google, Twitter, Instagram and the New York Times.

There is no clear timetable for when Facebook started looking for its way back into China. Facebook did not respond to an interview request. But in 2014, when Zuckerberg gave an entire speech in Mandarin to a group of students of Tsinghua University’s Economics and Management School, where he and Apple’s Tim Cook serve as advisory board members, many saw it as Zuckerberg showing his determination to conquer China and its roughly 700 million online netizens.

Later that year, Zuckerberg, in Seattle, told an official from China’s internet information office that he had been reading Xi’s book, Governance of China, and recommended it to his colleagues.

When Xi himself visited Seattle the next year as part of his first state visit to the United States, Zuckerberg was able to meet Xi and talked to him in Mandarin. He said on Facebook that it was his first time having a conversation with a world leader in a foreign language. Zuckerberg also reportedly asked Xi to come up with a name for his new-born child.

During his trip to China in 2016, Zuckerberg posted a photo of himself running in Tiananmen Square in Beijing. In the background was a portrait of Mao on the wall and a smoky sky, an indication of bad air quality.

The air pollution at the time made Beijing residents wear masks when they went outside. Even Xinhua, China’s official propaganda and news agency, was surprised by the fact that Zuckerberg did not wear any protections.

Unlike Google, who withdrew from mainland China to Hong Kong in 2010 because it refused to cooperate with the Chinese government on censoring certain search results, Facebook has reportedly created its own tool to do the censoring if required.

It’s not the first time that Facebook has censored content. But it usually does not take actions after certain posts were made. For China, Facebook will start censoring the content before it ever appears, like many China-originated social media, such as Weibo, a Chinese version of Twitter, and Wechat, an instant chatting app.

China has not been totally disconnected from Facebook. In fact, a lot of Chinese companies are using ads on Facebook to find international customers. But many of the companies are state-owned media. A recent Congressional report has urged the U.S. administration to list all reporters working for these media companies as spies.

This summer, Facebook launched an app called Colorful Balloons exclusively for the Chinese market to analyze how users interact with each other. Until now, Colorful Balloons has 118 reviews in China’s App Store. Weibo and Wechat respectively have 44,604 and 76,748.